1. Field of the Invention
This invention relates to method and apparatus for the production of hydrocarbons from geologic oil-bearing formations, and more particular, method and apparatus for enhancing the secondary recovery of oil from such formations.
2. Brief Description of the Prior Art
Oil has been recovered from geological oil bearing reservoirs through wells in a variety of ways. Where the reservoir contains sufficient pressure the oil may be forced out of the reservoir through a well without assistance. Pumps are also used to lift oil out of a well.
Many times a reservoir does not contain sufficient pressure to force the oil out of the reservoir into the well and secondary recovery techniques are required for recovery. One method widely used is to flood the reservoir from one or more injection wells to drive the oil from the reservoir to adjacent production wells from which the oil is lifted to the surface.
Flooding has been performed with a variety of fluid medium, including surfactants, water at normal temperatures, water at elevated temperatures and steam. Specially prepared fluids have been used to cause the oil to more easily move out of the formation.
Fracturing is a well known technique for enhancing the flow of fluid from injection wells and the flow of fluid from the reservoir into the production wells. Specifically, fluid has been forced through the opening in an injection well into the surrounding geological formation to fracture or open up the surrounding sands. Propping materials, such as sand particles, have been injected into the induced injection fracture to hold the fracture open and allow the fluids to flow more readily to the formation from the injection well. Similarly, fluids have been forced through the openings in a production well into the surrounding formation to fracture or open up the sands. Propping materials, such as sand particles, have been injected into the sands of the induced production fractures to hold the formation open to thereby allow the oil and other fluid in the surrounding formation to flow more easily into the production well.
U.S. Pat. No. 2,862,556 to Tek et al. discloses an example of such water flooding methods using an injection well and production well surrounded by fractures. The horizontal fracture is induced through and around the injection well at one level, preferably at a lower level or adjacent the bottom of the formation, whereas horizontal fractures are induced around the production wells at a higher level or adjacent the top of the formation. Production fractures overlap with the injection fracture. A water drive is applied through the lower injection fractures to the upper production fractures so as to lift the oil to the upper fracture. Tek points out that the direction of the drive may be reversed. Another U.S. Pat. No. 2,946,382 to Tek et al discloses flooding between horizontal overlapping injection and production fractures, using such media as hot combustible gas, hot water, super heated steam and other hot fluids.
U.S. Pat. No. 3,199,586 to Henderson et al discloses a method for increasing the amount of oil recovered in a water flood, between horizontally extending fractures of the type disclosed in the Tek patents. Specifically, Henderson discloses the use of water containing a surfactant to help flood the oil from the surrounding formation and allow it to flow more easily into the production well. Also disclosed is a method for creating a line of injection wells and a line of injection fractures, one in communication with each injection well. Spaced away in a somewhat parallel pattern is a line of production wells and a line of production fractures, one in communication with each production well. Fluid injected into the injection wells flows out into the vertically extending injection fractures, then across the formation into the vertical production fractures. No discussion or suggestion is made in Henderson that the two arrangements may be somehow combined.
U.S. Pat. No. 4,265,310 to Britton discloses a fracture preheat oil recovery process.
An article entitled Gravity Drainage of Oil Into Large Horizontal Fractures, by T.E. Morrisson, James H. Henderson, published in Trans of AIME VOL., 219, pages 2-15 (1960), discusses the production of oil through horizontal extending fractures of high capacity and large radius placed at the base of producing formations. Gravity drains the fluid into the producer fracture, and hence into the production well from which the fluid is lifted to the surface. This technique is satisfactory where the oil is of low viscosity for ease of flow, but has drawbacks where the oil has higher viscosities and the producing formation is then thin. Additionally, the recovery rate is slow since fluid flow depends principally on the flow of gravity.
Other articles have been written relating to hydraulic fracturing for the recovery of oil. For example, note the article entitled Application of Hydraulic Fracturing in the Recovery of Oil by Water Flooding: A Summary, by James Wasson, published by the Bureau of Mines Information Circular, 8175 (1963), the article Effects of Fractures Hydraulic in Oklahoma Water Flood Wells, by John P. Powell & Kenneth H. Johnson, published by the Bureau of Mines Information Circular, 5713 (1960), and the article The Street Ranch Pilot Test of Fracture-Assisted Steam Flood Technology, by Britton, Martin, Lebricht and Harmon, presented at the 1982 meeting of the SPE.
The Tek and Henderson methods disclosed above using horizontal overlapping production and injection fractures at, respectfully, the top and bottom of the well, apparently have not been commercially successful.